Use patching for dart:io.

runtime/bin/io_sources.gypi

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # This file contains all sources for the dart:io library.
 {
   'sources': [
-    # The io.dart file needs to be the first source file. It contains
-    # the library and import directives for the dart:io library. The
-    # dart:io library is created by concatenating the files listed here
-    # in the order they are listed.
-    'io.dart',
-
-    'base64.dart',
-    'buffer_list.dart',
-    'chunked_stream.dart',
-    'common.dart',
-    'directory.dart',
-    'directory_impl.dart',
-    'eventhandler.dart',
-    'file.dart',
-    'file_impl.dart',
-    'http.dart',
-    'http_impl.dart',
-    'http_parser.dart',
-    'http_session.dart',
-    'http_utils.dart',
-    'input_stream.dart',
-    'list_stream.dart',
-    'list_stream_impl.dart',
-    'mime_multipart_parser.dart',
-    'output_stream.dart',
-    'path.dart',
-    'path_impl.dart',
-    'platform.dart',
-    'platform_impl.dart',
-    'process.dart',
-    'process_impl.dart',
-    'socket.dart',
-    'socket_impl.dart',
-    'socket_stream_impl.dart',
-    'stdio.dart',
-    'stream_util.dart',
-    'string_stream.dart',
-    'timer_impl.dart',
-    'websocket.dart',
-    'websocket_impl.dart',
+    'common_patch.dart',
+    'directory_patch.dart',
+    'eventhandler_patch.dart',
+    'file_patch.dart',
+    'http_patch.dart',
+    'platform_patch.dart',
+    'process_patch.dart',
+    'socket_patch.dart',
+    'stdio_patch.dart',
   ],
 }